I'm a 12D in the loafers and 13B in the mocs. Rancourt customer service helped with sizing. Brannock is 13B. My feet are a bit wonky though - both are almost completely flat and my left is a full brannock size shorter than the right - so take my advice and experience with that in mind. Their lasts seem to work well for my feet which can be a challenge. Both were only about $120 new at their pre-sale too and at that price I can't complain, nicer than most options in that price range. Paying the full $320 MSRP may have been a different story though.
I agree with your thoughts on the shell though. If I'm going to pay for shell, I'd rather just grab the Alden LHS. Rancourt's are a bit rough and ready in styling in my experience, which isn't a bad thing for chromexcel and some of their moc-styled option but sort of defeats the purpose of buying shell for loafers. I'm not a huge fan of Rancourt's full strap and weltline loafers. The extra couple of hundred dollars for Alden is definitely worth it for those. I do like their more rugged offerings though (boots, mocs, beefrolls, etc.). I live in a more rugged place though, so the moc stylings work pretty well here.